Short Answer 
Mass is a constant measure of matter, while weight varies due to gravity; for example, a tub of margarine typically has a mass of 500 grams. Common household items like margarine are labeled with their mass, and bathroom scales measure weight but display it as mass based on gravity calculations.
Step 1: Understand Mass and Weight
The mass of an object is a measure of the amount of matter it contains, and is always constant regardless of location. For instance, a tub of margarine typically has a mass of 500 grams. On the other hand, weight is the gravitational force acting on that mass, which can change depending on where you are due to varying gravity levels.
Step 2: Identifying Common Items
When looking for items in your home that weigh exactly 500 grams, a tub of margarine is a perfect example, as it is commonly labeled with that weight. Remember that mass is represented as a single number, such as 500 g, making it clear and straightforward to identify everyday items with a known mass.
Step 3: Using Scales and Understanding Measurements
Bathroom scales measure the weight of an object but are usually calibrated to show mass. They do this by calculating the weight based on gravitational pull, typically at 9.80 m/s². Therefore, when you weigh your margarine tub and it shows 500 grams, the scale is reliably converting that gravitational force into a mass unit that you can understand and use in everyday situations.